Human coronaviruses cause 15 to 30% of common colds which are associated with economic losses worldwide. We recently discovered that the receptor for human coronavirus HCV-229E is a membrane glycoprotein called human aminopeptidase N (hAPN) or CD13. Several monoclonal antibodies directed against hAPN prevent virus from binding to hAPN and prevent infection. Our goal is to develop peptides or peptidomimetics that inhibit virus- receptor interactions and are sufficiently non-toxic that they can be used in the respiratory tract to prevent HCV-229E infection or reduce the shedding of infectious virus. To do this, we will use mutational analysis to identify the residues required for binding of the receptor with the virus glycoprotein and/or anti-hAPN MAbs. Peptides or other drugs targeted to these binding sites will be tested for their ability to block virus-receptor interactions and prevent infection of cultured cells. Because no animals are susceptible to HCV-229E infection, we will make transgenic mice expressing hAPN in the respiratory epithelial cells, and challenge them with HCV-229E virus intranasally. If they are susceptible to infection as predicted, then potential anti-human coronavirus drugs that are effective and non-toxic in vitro can be tested in vivo in these animals. We will also investigate the nature of the receptor for human coronavirus HCV-OC43 in order to develop receptor-targeted anti-viral drugs that could be used in combination with drugs that block interactions of HCV-229E and human rhinoviruses with their specific receptors. A combination drug like this would be suitable for more than 90% of common colds in man. The mouse coronavirus MHV, which is closely related to HCV- OC43, is an important model for coronavirus infection in its natural host. Molecular interactions of MHV spike glycoprotein with isoforms of the biliary glycoprotein that serve as the MHV receptor (MHVR) will be studied with biosensor, genetic and structural techniques. The resulting three dimensional structural data will be used to generate candidate drugs to prevent or treat MHV infection of the respiratory or enteric tracts. These will be tested for efficacy and toxicity in vitro and then in vivo. These detailed studies of coronavirus-receptor interactions are also expected to elucidate the effects of receptors upon the virus attachment glycoproteins and provide new insight into the early steps of coronavirus attachment and penetration into cells.